BACKGROUND. Hypophosphatasia (HPP) is a rare genetic disorder resulting in variable alterations of bone formation and mineralization that are caused by mutations in the ALPL gene, encoding the tissue-nonspecific alkaline phosphatase (ALP) enzyme.
METHODS. In this phase IIA open-label, single-center, intra-patient, dose-escalating study, adult patients with HPP received 3 ascending intravenous doses of 5, 10, and 20 mg/kg BPS804, a fully human anti-sclerostin monoclonal antibody, on days 1, 15, and 29, respectively. Patients were followed for 16 weeks after the last dose. We assessed the pharmacodynamics, pharmacokinetics, preliminary efficacy, and safety of BPS804 administrations at specified intervals during treatment and follow-up.
RESULTS. Eight patients (mean age 47.8 years) were enrolled in the study (6 females, 2 males). BPS804 treatment increased mean ALP and bone-specific ALP enzymatic activity between days 2 and 29. Transient increases in the bone formation markers procollagen type-I N-terminal propeptide (PINP), osteocalcin, and parathyroid hormone as well as a transient decrease in the bone resorption marker C-telopeptide of type I collagen (CTX-1) were observed. Lumbar spine bone mineral density showed a mean increase by day 85 and at end of study. Treatment-associated adverse events were mild and transient.
CONCLUSION. BPS804 treatment was well tolerated and resulted in increases in bone formation biomarkers and bone mineral density, suggesting that sclerostin inhibition could be applied to enhance bone mineral density, stability, and regeneration in non-life-threatening clinical situations in adults with HPP.
Geometric mean plots of bone biomarkers. After infusion of BPS804, transient increases in bone formation markers (A) PINP (maximum 101% on day 43) and (B) OC (maximum 92% on day 43) were detected. (C) There was a concomitant transient decrease in the bone resorption marker CTX-1 (maximum –35% on day 36). (D) The bone formation biomarker PTH also showed an increase (maximum 60% on day 57) in the study.